Lead frame packaging is a well known methodology for packaging microchips. Lead frames are generally etched or stamped from a metal, such as copper, to form the lead frame. The lead frame typically includes a plurality of leads (“legs”) to be used for input and output of one or more microchips along with a platform for attaching one or more microchips. The platform is generally conductive and referred to as a paddle or die pad. Microchips are attached to the paddle using a die attach material. Die attach material has an uncontrolled thickness. The die attach material is applied to the paddle in a liquid state and the microchips are pressed into the liquid die attach. The die attach spreads on the paddle in a non-uniform manner during placement of the microchips. The die attach material is then cured into a solid form. During curing, from a liquid to a solid phase, the die attach material hardens and is prone to developing voids due to trapped air bubbles. The microchips are then wire bonded to the leads and sometimes also wire bonded to each other prior to encapsulation with an insulative material, such as plastic molding compound.
Problems with lead frame design can arise, however, when unintended currents leak between two adjacent microchips along the platform supporting the microchips. Since the die attach material is non-uniform in thickness and may develop voids due to air bubbles during curing, the die attach material has non-uniform isolation properties. Two adjacent microchips on a single die paddle may leak current onto the die paddle due to the non-uniform nature of the die attach material. Undesirably, leakage currents may adversely affect the microchips and the overall device functionality and reliability. For example, a first microchip may produce a leakage current that is received by a second, adjacent microchip. This problem is exasperated by microchips employing large voltage potentials (e.g. 100s to 1000s of volts). With large voltage potentials, arching between microchips may occur even if the microchips are spatially separated.
The art has responded to these problems by providing split (i.e., multiple), properly spaced electrically isolated die paddles. Accordingly, one microchip couples with one die paddle while the other microchip couples with the other die paddle. In fact, to accommodate more than two microchips, some packages have more than two paddles. Chip package designers isolate the chips by separating the chips by a gap and providing a mold material that forms around the microchips with a sufficient dielectric insulation capacity to isolate the two or more microchips.
Although generally effective at substantially mitigating/eliminating leakage current problems, split paddles are more complicated to produce and thus, more costly. For example, many applications provide split paddles as a custom engineering solution, thus increasing production costs. Split paddle designs require a custom etching for the lead frame or a specialized stamp. If the microchips change, for example, to a larger microchip, the paddle design must also be changed.